1. Field of the Invention
The present invention relates to a method for starting a synchronous machine.
2. Description of the Related Art
Various methods are known, for example from published U.S. Patent Application Publication US 2007/0170880 A1, for controlling electric machines, for example permanent-magnet synchronous machines. The control of electric machines requires a knowledge as accurate as possible of the rotor position of the electric machine, which may be ascertained by using a digital sensor system, for example.
When a digital sensor system is used, it is disadvantageous that only an approximate position of the rotor may be estimated at a standstill. At very low rotational speeds, in particular for dynamic acceleration processes, it is not possible to adequately estimate the rotor position for good current control and torque control due to the time interval between two digital sensor signals. As a result, use of a digital sensor system for determining the rotor position with an acceptable level of convenience is possible only for drive trains having a sliding clutch or a hydraulic converter between the electric machine and the wheels of the vehicle. In particular for drive trains having a low gear ratio of the electric machine with respect to the wheel, the currently existing control problems in the form of torque surges and noise generation are very noticeable.